The present invention relates generally to semiconductor manufacturing and more particularly to a method for thinning a semiconductor substrate.
Semiconductor devices made from gallium arsenide (GaAs) substrates are capable of increased performance over those made from silicon substrates. GaAs has a larger low-field electron mobility and a lower saturation field than silicon; and GaAs can be made semi-insulating, which reduces parasitic capacitance. All of which mean an increase in speed as compared to silicon.
However, compared to silicon, Gallium arsenide is a poor thermal conductor. This limits the number of integrated circuits that can be fabricated on a given area of semiconductor material and limits the power capability of the semiconductor device. To improve thermal conductivity, GaAs device substrates are typically thinned. This involves mechanically grinding away bottom portions of the gallium arsenide substrate after forming the semiconductor device. The grinding process can cause problems with substrate breakage, and the performance variations associated with grinding result in considerable within-wafer and wafer-to-wafer thickness variations. Conventional grinding processes can thin GaAs substrates to target thicknesses of approximately 25 microns and are capable of achieving uniformities of +/xe2x88x9213 microns across the wafer (i.e., for a substrate having a target thickness of 25 microns after grinding, the thickness across the substrate can range from approximately 12-38 microns). Additional thinning of the wafer substrate to accommodate increased thermal conductivity and power requirements will ultimately require wafer thinning processes that have improved uniformity and are less susceptible to breakage.